The invention relates to flame retardant polycarbonate resin compositions and articles made therefrom having high transparency.
Polycarbonate resin compositions are used in a variety of fields including automobiles, electric, electronic, machinery, building and construction applications and the like. Resins used for some of the above-mentioned applications must pass strict flame retardancy requirements, e.g., the flame-retardancy standard according to UL-94 in the U.S.A. Such tests typically involve exposing an object made from the resin to a flame or other heat source for a certain time period. The object may fail the test by catching fire, remaining on fire for too long a period, or by partially melting and dripping flaming resin droplets on a flammable material placed below the object. In some applications requiring miniaturization and/or very thin molded articles, there is an increased risk of a flaming dropletarising from the thinned part of the shaped article. Resins used in such applications need to fulfill the requirements for obtaining a V0-rating according UL-94, i.e. short flame-out times ( less than 10 s) and no (burning) drips that ignite alayer of cotton placed beneath the object.
Satisfactory UL94 V0-ratings of polymers do not always guarantee a good fire performance in building and construction applications. One reason for this discrepancy is the duration requirements for the UL94 tests. In fire tests for the building and construction areas, exposure time to an heat source (i.e. open flame or radiant panel) is in the order of minutes (equal to or more than 5 minutes), while UL94-testing requires much shorter exposure times (2 times 10 seconds).
In certain building and construction applications, there are various government-mandated tests, each with its own specifications and requirements, for evaluating the fire resistance of thermoplastics. A European Single Burner Item (SBI) test has been developed to harmonize the different national standards and better measure fire performance of construction products. This test is defined to cover all important parameters of the various country-specific tests, some of which are speed of flame spread, time to ignition, height of flames, smoke production and production of burning droplets. The formation of burning droplets is critical for passing the French test norm NF-P-92-501 and for determining the overall rating (M1-M4) for the material and application. The formation of droplets is measured in French test norm NF-P-92-505 (also known as the xe2x80x9cdripping testxe2x80x9d) and this test, is considered to be one of the more aggressive tests for fire performance of building and construction materials.
Prior art flame retardant systems for polycarbonate compositions typically employ phosphates and halogens. The phosphates lower the use temperature of the polycarbonate as well as its impact strength. As pointed out by various environmental protection groups, the use of halogens possibly generates toxic fumes when a resin composition burns. Therefore, there is need for an improved flame-retardant resin composition.
Guanidine salts are known to impart flame retardant characteristics to resins used in various applications. JP Patent No. 8603995 discloses the addition of 1-30 wt. % guanidine cyanurate in various resin compositions including polyester, nylon, polycarbonate, epoxy, phenol, and polyurethane. U.S. Pat. No. 4,341,694 discloses compositions displaying intumescent and flame retardant characteristics comprising: a resin selected from polyolefins, polyvinylaromatic resins, polycarbonates, polyacrylates, polyamides, PVC and blends thereof; and about 20-60% by weight of a) a bicyclic phosphate compound, and b) a nitrogen compound selected from the group including guanidine and salts thereof.
Applicants have surprisingly found that guanidine inorganic salts, when added to a polycarbonate resin composition, surprisingly and dramatically increase its pass rate in a specific dripping test, while still retaining its transparent characteristics and other properties.
The invention is directed to a thermoplastic resin composition consisting essentially of: a) an aromatic polycarbonate resin; and b) a flame retarding amount of a guanidine salt. In one embodiment of the invention, the guanidine salt is selected from the group consisting of guanidine inorganic salts and mixtures thereof. In a second embodiment, the guanidine salt is selected from the group consisting of guanidine carbonate, guanidine hydrochloride, guanidine bisulfite, guanidine sulfate, guanidine sulfamate, guanidine phosphate, guanidine hydrobromide, and mixtures thereof.
The invention further relates to a method to improve the pass rate in a specific dripping fire test of a thermoplastic resin composition by adding a flame retarding amount of a guanidine salt to said thermoplastic resin composition.
As used herein, xe2x80x9cflame retardingxe2x80x9d amount means an amount sufficient to improve the results observed when conducting the dripping test.
As used herein, xe2x80x9ca sufficiently large numberxe2x80x9d in the context of obtaining a 50% higher dripping test pass rate for samples containing a guanidine salt, derivatives or mixtures thereof refers to the fact that for very small numbers of samples a reduction in pass rate may not be statistically significant, and that a sufficient number of samples must be observed to draw statistically valid conclusions.
Polycarbonate Resin Component. Aromatic polycarbonate resins suitable for use as the polycarbonate component of the composition of the present invention are known compounds whose preparation and properties have been described, see, generally, U.S. Pat. Nos. 3,169,121, 4,487,896 and 5,411,999. In one embodiment, they are polymers having repeating units with a structure of a general formula (I) as follows: 
In the formula, X1 and X2 each represent a hydrogen atom or a linear, branched or cyclic alkyl group having from 1 to 6 carbon atoms. The alkyl group may include, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-amyl group, an isoamyl group, an n-hexyl group, an isohexyl group, a cyclopentyl group, and a cyclohexyl group. These X1 and X2 may be the same or different. xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d each indicate the number of the substituents, and they are each an integer from 0 to 4. Where the polymer has plural X1""s and X2""s, said plural X1""s may be the same or different; and where it has plural X2""s, said plural X2""s may be the same or different.
Also in the formula, Y represents a single bond, an alkylene group having from 1 to 8 carbon atoms (e.g., methylene, ethylene, propylene, butylene, pentylene, hexylene, etc.), an alkylidene group having from 2 to 8 carbon atoms (e.g., ethylidene, isopropylidene, etc.), a cycloalkylene group having from 5 to 15 carbon atoms (e.g., cyclopentylene, cyclohexylene, etc.), a cycloalkylidene group having from 5 to 15 carbon atoms (e.g., cyclopentylidene, cyclohexylidene, etc.), xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, or a bond of a formula (II-1) or (II-2): 
The above-mentioned polymers can be produced generally by reacting a diphenol of a general formula (III) with a carbonate precursor such as phosgene or a carbonate compound, and wherein the molecular weight of the polymers can be established in a known manner with an appropriate quantity of known chain terminators. 
wherein X1, X2, Y, a and b are each as previously defined.
The diphenol of formula (III) includes various diphenols. In one embodiment, the diphenol is 2,2-bis(4-hydroxyphenyl)propane [bisphenol A]. Others include bis(4-hydroxyphenyl)alkanes such as bis (4-hydroxyphenyl)methane, 1,1-bis (4-hydroxyphenyl)ethane, 1,2-bis(4-hydroxyphenyl)ethane; bis(4-hydroxyphenyl)cycloalkanes such as 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)cyclodecane; and also 4,4xe2x80x2-dihydroxydiphenyl, bis(4-hydroxyphenyl)oxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)ketone, etc. In addition to these, also mentioned is hydroquinone. These diphenols may be used singly or as combined.
Chain terminators or molecular weight regulators may be any and every one generally used in production of ordinary polycarbonates. For example, they can be phenol, long-chain alkyl phenols, monoalkylphenyls, or dialkyl phenols such as p-cresol, p-tert-butylphenol, p-tert-octylphenol, p-cumylphenol, or nonylphenol.
Polycarbonate resins of the present invention are made by known methods, such as, for example, interfacial polymerization, melt polymerization, solution polymerization or solid state polymerization. In the interfacial polymerization method wherein phosgene is used as a carbonate precursor, the diphenol is generally dissolved in an aqueous solution of an acid binder such as sodium hydroxide or potassium hydroxide and reacted with phosgene in a solvent such as methylene chloride.
In the melt transesterification method, the diphenol is transesterified with a carbonate compound in the presence or absence of a solvent and in an inert gas atmosphere and preferably in the presence of a catalyst. The carbonate precursor for use in the melt transesterification method is one or more of a carbonyl halide, a carbonate ester or a haloformate. Suitable carbonyl halides include, for example, carbonyl bromide and carbonyl chloride. Suitable carbonate esters include, for example, diphenyl carbonate, dichlorophenyl carbonate, dinaphthyl carbonate, phenyl tolyl carbonate and ditolyl carbonate. Suitable haloformates include, for example, bishaloformates of a dihydric phenol, such as, for example, hydroquinone, or glycols, such as, for example, ethylene glycol, neopentyl glycol. In one embodiment, the carbonate precursor is diphenyl carbonate.
It is also possible to employ aromatic polycarbonates resulting from the polymerization of two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with a hydroxy- or acid-terminated polyester or with a dibasic acid or with a hydroxy acid or with an aliphatic diacid in the event a carbonate copolymer rather than a homopolymer is desired for use. Generally, useful aliphatic diacids have from 2 to about 40 carbons. A preferred aliphatic diacid is dodecandioic acid. Polyarylates and polyester-carbonate resins or their blends can also be employed.
The polycarbonate resin component of the present invention may be either homopolymers comprising one type of diphenol, or copolymers comprising two or more types of diphenols. They may also be thermoplastic, random-branched polycarbonate resins comprising polyfunctional aromatic compounds along with monophenols, as well as blends of linear polycarbonate and a branched polycarbonate. They may also be polycarbonate-polyorganosiloxane copolymers comprising organosiloxane blocks having a degree of number-average polymerization of 5 or more. They may also be mixtures comprising two or more different polycarbonate resins.
The branched polycarbonates may be prepared by adding a branching agent during polymerization. These branching agents are well known and may comprise polyfunctional organic compounds containing at least three functional groups, which may be hydroxyl, carboxyl, carboxylic anhydride, haloformyl and mixtures comprising at least one of the foregoing. Specific examples include trimellitic acid, trimellitic anhydride, trimellitic trichloride, tris-p-hydroxy phenyl ethane, isatin-bis-phenol, tris-phenol TC (1,3,5-tris((p-hydroxyphenyl)isopropyl)benzene), tris-phenol PA (4(4(1,1-bis(p-hydroxyphenyl)-ethyl)alpha,alpha-dimethyl benzyl)phenol), 4-chloroformyl phthalic anhydride, trimesic acid and benzophenone tetracarboxylic acid, and the like. The branching agents may be added at a level of about 0.05 to about 2.0 weight percent. Branching agents and procedures for making branched polycarbonates are described in U.S. Pat. Nos. 3,635,895 and 4,001,184. All types of polycarbonate end groups are contemplated as being within the scope of the present invention.
Copolyester-carbonate, also known as polyestercarbonates, resins are also suitable for use as the aromatic polycarbonate resin component of the present invention. They are linear or randomly branched polymers resins which contain, in addition to recurring polycarbonate chain units, recurring carbonate groups, carboxylate groups and aromatic carbocyclic groups in the polymer chain, in which at least some of the carbonate groups are bonded directly to the ring carbon atoms of the aromatic carbocyclic groups. Copolyester-carbonate resins suitable for use as the aromatic polycarbonate resin component of the thermoplastic resin composition of the present invention are known compounds whose preparation and properties have been described, see, generally, U.S. Pat. Nos. 3,169,121, 4,430,484 and 4,487,896.
In one embodiment of the invention, the polycarbonate resins have a weight-average molecular weight of from 10,000 to 200,000. In another embodiment, they have a weight-average molecular weight from 15,000 to 50,000, for desirable mechanical strength properties, especially Izod impact strength and moldability.
In another embodiment of the invention, the polycarbonate resins are blends of two or more polycarbonate polymers or copolymers, in which case the weight average molecular weight Mw of the polycarbonate component is the molecular weight of the resulting polycarbonate polymer blend.
In yet another embodiment of the invention, the polycarbonate resin further comprises a graft copolymer component. Said graft copolymer component comprises a graft portion formed from at least two ethylenically unsaturated monomers and a rubbery polymer substrate. Suitable substrates include polymers and copolymers of one or more conjugated dienes, copolymers of conjugated dienes and non-diene vinyl monomers, alkylacrylate polymers, and copolymers of ethylenically unsaturated olefins and nonconjugated diene polymer (EPDM) rubbers. In one embodiment of graft copolymers, the substrate polymers comprise polybutadiene, polybutadienestyrene, polybutylacrylate and ethylene-propylenenorborene polymers. In another embodiment, the substrate polymer forming the graft component comprises polybutadiene.
In another embodiment of the invention, the polycarbonate resin component could also be a mixture of polycarbonate with other thermoplastic resins including but not limited to polystyrenes, polyolefins, aromatic polyesters, and (cyclo)aliphatic polyesters.
Guanidine Salt or Derivative Component. Guanidine salts or derivatives suitable for use in the present invention include, for example, aminoguanidine nitrate (AGN), guanidine nitrate (GN), triaminoguanidine nitrate (TAGN), guanidine BPA, diaminoguanidine nitrate (DAGN), guanidine carbonate, guanidine hydrochloride, guanidine bisulfite, guanidine sulfate, guanidine sulfamate, guanidine phosphate, guanidine hydrobromide, and mixtures thereof. In one embodiment, the guanidine salt is an inorganic salt. In one embodiment of inorganic salts, the salt is guanidine sulfate. In another embodiment, the guanidine inorganic salt is guanidine carbonate.
The amount of guanidine salt used is an amount sufficient for desirable flame retardant properties. In one embodiment, this amount is less than 1 wt. %. In another embodiment, it is about 0.001 to about 0.5 part by weight of the total weight of the composition (wt. %) to pass the dripping test. In yet another embodiment, the flame retarding amount is about 0.001 to 0.01 wt. %. In one embodiment, to optimize the distribution and dispersion of the guanidine sulfate salt in the polycarbonate the guanidine sulfate is dissolved in demineralized water before being added to the polycarbonate.
Other Components. The resin composition of the present invention may also be admixed with traditional halogen-free flame retardants in the prior art as well as variously known and used processing additives, so far as said additives do not interfere with the objects of the invention.
The additives may be used alone or in combination. As used herein, additives may include such materials as whitening agents, thermal stabilizers, antioxidants, light stabilizers, plasticizers, colorants, impact modifiers, extenders, antistatic agents, mold releasing agents, additional resins, blowing agents, and processing aids. The different additives that can be incorporated in the compositions are commonly used and known to one skilled in the art. Illustrative descriptions of such additives may be found in R. Gachter and H. Muller, Plastics Additives Handbook, 4th edition, 1993.
Examples of thermal stabilizers include triphenyl phosphite, tris-(2,6-dimethylphenyl)phosphite, tris-(2,4-di-t-butyl-phenyl) phosphite, tris-(mixed mono-and di-nonylphenyl)phosphite, dimethylbenzene phosphonate and trimethyl phosphate. Examples of antioxidants include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Examples of light stabilizers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole and 2-hydroxy-4-n-octoxy benzophenone.
Examples of plasticizers include dioctyl-4,5-epoxy-hexahydrophthalate, tris-(octoxycarbonylethyl)isocyanurate, tristearin and epoxidized soybean oil. Examples of the antistatic agents include glycerol monostearate, sodium stearyl sulfonate, and sodium dodecylbenzenesulfonate. Examples of mold releasing agents include pentaerythritol tetrastearate, stearyl stearate, beeswax, montan wax, and paraffin wax. Examples of other resins include but are not limited to polypropylene, polystyrene, polymethyl methacrylate, polyphenylene oxide, and polyesters, both aromatic and (cyclo)aliphatic.
Preparation The production of the compositions of the present invention may utilize any of the blending operations known for the blending of thermoplastics, for example blending in a kneading machine such as a Banbury mixer or an extruder. The sequence of addition is not critical but all components should be thoroughly blended.
To prepare the resin composition, the components may be mixed by any known methods. Typically, there are two distinct mixing steps: a premixing step and a melt mixing step. In the premixing step, the dry ingredients are mixed together. The premixing step is typically performed using a tumbler mixer or ribbon blender. However, if desired, the premix may be manufactured using a high shear mixer such as a Henschel mixer or similar high intensity device. The premixing step is typically followed by a melt mixing step in which the premix is melted and mixed again as a melt. Alternatively, the premixing step may be omitted, and raw materials may be added directly into the feed section of a melt mixing device, preferably via multiple feeding systems. In the melt mixing step, the ingredients are typically melt kneaded in a single screw or twin screw extruder, a Banbury mixer, a two roll mill, or similar device.
In one embodiment, the composition is used as a masterbatch. In this case, a masterbatch is first produced by melt mixing a relatively high amount of the ingredients into the carrying polymeric matrix. Thereafter the masterbatch is added in a small portion to polymer.
The properties of the composition of the present invention make it suitable for use in building and construction industries, especially for use in a variety of glazing applications, for example, roofs, greenhouses, sun rooms, swimming pool enclosures, and the like.
The composition may be shaped into a final article by various techniques known in the art such as injection molding, extrusion, gas assist blow molding, or vacuum forming. In one embodiment, the final article is in the form of extruded sheets, e.g. solid sheets, multi-wall sheets, and profiled sheets,. There is no particular limitation on the composition of additional layers used to form coextruded sheets. There is no particular limitation on the structure or geometry of the multi-wall sheets. In one embodiment, the article in the form of layers may comprise, for example, fluorescing agents to facilitate manufacturing and/or ultraviolet light absorbers to improve weatherability of the final araticle. The extruded solid sheets typically have a weight from about 0.5 to about 15 kilograms per square meter, and typically have a thickness from about 0.5 mm to about 15 mm, preferably from about 1 mm to about 12 mm. The extruded multi-wall sheets typically have a weight from about 0.5 to about 8 kilograms per square meter, and typically have a thickness of about 2 to about 50 mm, preferable from about 4 to about 40 mm.